Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $83.81   10.444%   $92.5631   $92.56   $92.55   $92.60  
  Purchase #2 $186.98   6.723%   $199.5507   $199.55   $199.55   $199.60  
  Purchase #3 $130.65   5.422%   $137.7338   $137.73   $137.75   $137.70  
  Purchase #4 $182.78   10.446%   $201.8732   $201.87   $201.85   $201.90  
  Purchase #5 $55.38   5.217%   $58.2692   $58.27   $58.25   $58.30  
  Purchase #6 $140.89   13.228%   $159.5269   $159.53   $159.55   $159.50  
  Purchase #7 $226.73   12.276%   $254.5634   $254.56   $254.55   $254.60  
  7 purchase totals = $1,007.22       $1,104.0803   $1,104.07   $1,104.05   $1,104.20